This invention relates to an improved digging tooth arrangement for use in a bucket wheel excavator having buckets with replaceable center, corner and side teeth.
Excavators of this type are conventionally adapted to excavate the ground or rock by means of buckets provided on a rotating wheel so as to be moved around an arc. The buckets in order to be efficient in operating on hard rock or when used for dredging have to be equipped with digger teeth which in regard to their configuration and arrangement must be adapted to suit the particular cutting action and must be capable of continuously clearing the wheel. To meet these requirements it is common practice to employ center, corner and side teeth of different formations and dimensions; see "Der Schaufelradbagger als Gewinnungsgerat" (Bucket Wheel Excavator applied as a Winning Machine), 1st edition 1973, TRANS. TECH. PUBLICATIONS, page 121.
This known construction and arrangement involves, however, high storage costs and maintenance handicaps. A further disadvantage resides in their screwed connection with the bucket wall, as this besides weakening the material renders the replacement of the digger teeth difficult, since the fastening screws are located close to the material to be excavated.
It is an object of the present invention to improve the arrangement of digger teeth on the buckets of a bucket wheel excavator. Another object of the invention is to provide a digger tooth of novel construction suitably configured and arranged on a bucket so as to permit more efficient operation on hard rock and in dredging as has hitherto been possible, yet presenting a longer useful life and reduced assembly and maintenance times.
To achieve these objects, the invention provides a digger tooth arrangement of the type specified wherein the center, corner and side digging teeth are identical in configuration and dimensions, the center axes of one or more of the center teeth arranged in one or more perpendicular section planes cutting the bucket in the center or equally spaced thereto are disposed normal to the upper edge of the bucket, wherein the center axes of the corner teeth disposed in the plane comprising the front wall of the bucket are positioned so as to include equal, but opposed angles with the upper edge of the bucket and wherein the center axes of the side teeth arranged in the plane comprising the side walls of the bucket are positioned so as to respectively include unequal angles oriented in the same direction with the respect to the upper edge of the bucket.
According to a further features of the invention the inclination angle of the corner teeth is 10.degree. to 20.degree., preferably 15.degree., and the angles of inclination of the side teeth increase respectively by 5.degree. within a range of 5.degree. to 20.degree., preferably to obtain 5.degree., 10.degree. and 15.degree..
It is particularly advantageous if the angular position of the digger teeth which are removably secured to the front wall of the bucket includes an angle .alpha. (alpha) in the range of 30.degree. of 50.degree., preferably 43.degree., and a clearance angle .gamma. (gamma) in the range of 20.degree. to 28.degree., preferably 23.degree., while the angle .alpha. (alpha) included by the digger teeth removably secured to the side walls ranges from 30.degree. to 50.degree., preferably 48.degree., the clearance angle .gamma. (gamma) ranging from 20.degree. to 28.degree., preferably 18.degree..
The digger teeth are suitably secured in sockets welded to the outer walls of the bucket, the inner walls of the sockets being adapted to receive the complementary shaped outer surfaces of the shank of the digger tooth.
According to a further feature of the invention the digger tooth formed as an integral part comprises a tooth base and a tooth shank with a bead serving as an abutment disposed therebetween, said tooth base having a bottom portion which with respect to a planar contact surface of the tooth shank presents a surface positively inclined by 1.degree. to 3.degree., preferably 2.degree., whereas the upper portion of the tooth base with respect to said contact surface presents a surface negatively inclined by 20.degree. to 25.degree., preferably 23.degree., the rake angle of the tooth base being 19.degree. to 22.degree., preferably 21.degree..
The tooth shank according to the invention is a truncated pyramid forming an irregular hexagon base and having two planar surfaces disposed opposite to each other, one of said surfaces forming the perpendicular contact surface with respect to the pyramid base, whereas the further surfaces of the truncated pyramid are disposed relatively opposite each other in pairs to include an angle of about 168.degree., said tooth base in the area directed away from said cutting edge essentially forming a double T section, so that recesses between the legs of said double T are provided on the upper portion and on the bottom portion of said tooth base.
To removably fasten the digger tooth on the bucket wall the contact surface of the digger tooth is provided with a projection to be engaged by a retaining lug, said retaining lug by means of a threaded bolt extending through the end of the socket away from the digger tooth and carrying a closure cap, said closure cap being secured by means of a lock nut to the adjacent end of said socket.
For special applications it is preferred to configure the tooth base of the digger tooth according to the present invention as a pointed tooth of cross-shaped section.
Due to the novel configuration of the digger teeth and the selection of predetermined angular positions of these teeth, it is now possible to devise an arrangement which uses identical digger teeth for any of the center, corner and side teeth and which takes into account the specific requirements of different cutting actions by an appropriate selection of the angular position of the digger teeth with respect to the upper edge of the respective bucket and of the inclination of the sockets in which the teeth are received.
Considering that a conventional excavator of the type referred to generally comprises about fifteen buckets, each being equipped with nine digger teeth, it will readily be appreciated that the application of identical digger teeth considerably simplifies the manufacture of the digger teeth and facilitates their assembly and maintenance. Since the sockets supporting the digger teeth are welded to the respective bucket, the possibility of false mounting when replacing the digger teeth is prevented. To ensure proper welding of the sockets to the outer walls of the bucket, mounting surfaces are provided. The bead provided in accordance with the invention completely covers the upper end of the socket to protect it against wear and clogging. The arrangement of the retaining elements at the rearward end of the socket and on the side away from the tooth base prevents these elements from being damaged by the material to be excavated, thus rendering their disconnection easier than before. Finally, by proper selection of the cutting and clearance angles perfect clearance of the wheel is ensured even under severe operating conditions, with the result of increased removal rates.